The number of neurotransmitter receptors at a synapse has a profound effect on the excitability of that neuron. The mechanisms that govern the number of receptors expressed remain largely unknown. An understanding of these processes is basic to an understanding of the dynamic molecular architecture of a synaptic circuit. It is well established for several neurotransmitter receptors that the number of surface receptors is drastically affected in both disease and drug addicted states. This proposal describes a basic approach to investigating the relationship between the animo acid sequence of a receptor subunit and the number of receptors expressed on the cell surface. The strategy described in this proposal is based on the fact that two homooligomeric ligand-gated ion channels are expressed o the surface of cells at vastly different levels. In contrast to the serotonergic 5HT3 receptor (5HT3R), the alpha7 nicotinic acetylcholine receptor (nAChR) is poorly expressed on the surface of cells transfected with cDNA encoding this subunit. The majority of receptor protein resides intracellularly. Alpha-bungarotoxin is a high affinity ligand for the alpha7 nAChR. The number of (125)-I-alpha-bungarotoxin sites increases on the surface of cells expressing a chimeric alpha7-5HT3 receptor subunit. These observations prompt the hypothesis: Amino acid sequence within the subunits of ligand-gated ion channels determine surface receptor expression. The specific aim or this research proposal is to identify the subunit domain within a ligand-gated ion channel that are determinants of surface receptor expression. GRANT-F33DE05679 Osseointegration and Ti-based materials have greatly expanded the clinical repertoire of the oral health professional. Similarly, total joint arthroplasty has revolutionized treatment of end-stage arthritis. Both dental and orthopedic implants rely on anchorage in bone, and loss of fixation secondary to periimplant bone resorption is the major cause of implant failure. Although Ti-based materials exhibit biocompatibility in bulk, in particulate form they may elicit inflammatory responses leading to osteolysis. There appears to be no difference in cell response between bulk cpTi and Ti-alloys, but evidence suggests that a differential response exists for particles of cpTi and Ti-alloy. Previous studies have not thoroughly characterized particulate metals; the specific aims of this work are to evaluate the effects of particle size, shape, composition, and surface charge on cellular responses in vitro. Particles of cpTi, Ti-6A1-4V, and silica will be characterized by laser light scattering, sedimentation, profile analysis, Auger spectroscopy, SIMS, and zeta potential. A tissue culture system based on human macrophages and fibroblasts will be utilized, and media from treated cells assayed for products implicated in pathologic bone resorption.